1. Field of the Invention
The present invention relates to a piston with a ceramic piston head, and more specifically the invention relates to a piston with a piston head made of ceramics and having a rounded thread portion at the outer periphery thereof.
2. Description of the Related Art
Heretofore, ceramic sintered bodies having a heat resistance and a low heat conductivity have been used in piston heads of the internal combustion engines to reduce heat loss, improve fuel consumption, reduce the amount of discharge of hydrocarbons, carbon monoxide, etc., and enhance the output during engine operation. For this purpose, there have been various proposals with respect to methods of assembling a piston body of a light alloy as an ordinary material and ceramic piston head together, and the configuration and the structure of ceramic piston heads.
However, since there is a large difference in the coefficient of thermal expansion between the ceramic material used in the ceramic piston head and the light alloy used as the piston body, conventional pistons have the drawback that the fixture between the metal piston body and the ceramic piston head is loosened during the engine operation or a local stress acts upon the ceramic piston head during the reciprocal movement of the piston at a high speed, so that the piston head is likely to be broken due to the brittleness of ceramics. Further, the structure of the ceramic piston head is complicated to assuredly fix the ceramic piston head to the metal piston body, so that there is a practical problem in that the manufacture is difficult due to inherently difficult working of the ceramics.